Previous studies have shown that high titers of antisperm antibodies are correlated with low fertility. Furthermore, immunosuppressive therapy enhances pregnancy in some individuals. Serum tests, however, provide only an indirect measure of a potential pool of antisperm antibodies. When men have antibodies, direct measurement of the percent of sperm that are entirely antibody bound is a more appropriate approach. Antibodies can affect fertilization at many sites. Since sperm are composed of numerous antigens, many antibodies can develop but not all of them will interfere with infertility. Better tests are necessary to define which antibodies may affect fertility. To do that requires the development of better antigens. Use of monoclonal antibodies allows a framework for such further modifications.